The sodium iodide symporter (NIS) as an imaging reporter for gene, viral, and cell-based therapies.

Penheiter AR, Russell SJ, Carlson SK - Curr Gene Ther (2012)

Bottom Line:
There are several reporter systems available; however, those employing radionuclides for positron emission tomography (PET) or singlephoton emission computed tomography (SPECT) offer the highest sensitivity and the greatest promise for deep tissue imaging in humans.Within the category of radionuclide reporters, the thyroidal sodium iodide symporter (NIS) has emerged as one of the most promising for preclinical and translational research.NIS has been incorporated into a remarkable variety of viral and non-viral vectors in which its functionality is conveniently determined by in vitro iodide uptake assays prior to live animal imaging.

ABSTRACTPreclinical and clinical tomographic imaging systems increasingly are being utilized for non-invasive imaging of reporter gene products to reveal the distribution of molecular therapeutics within living subjects. Reporter gene and probe combinations can be employed to monitor vectors for gene, viral, and cell-based therapies. There are several reporter systems available; however, those employing radionuclides for positron emission tomography (PET) or singlephoton emission computed tomography (SPECT) offer the highest sensitivity and the greatest promise for deep tissue imaging in humans. Within the category of radionuclide reporters, the thyroidal sodium iodide symporter (NIS) has emerged as one of the most promising for preclinical and translational research. NIS has been incorporated into a remarkable variety of viral and non-viral vectors in which its functionality is conveniently determined by in vitro iodide uptake assays prior to live animal imaging. This review on the NIS reporter will focus on 1) differences between endogenous NIS and heterologously-expressed NIS, 2) qualitative or comparative use of NIS as an imaging reporter in preclinical and translational gene therapy, oncolytic viral therapy, and cell trafficking research, and 3) use of NIS as an absolute quantitative reporter.

Figure 4: Micro-SPECT/CT imaging of an orthotopic transplantation model of pancreatic cancer. BxPC-3-NIS xenograft fragments weretransplanted to the pancreas of donor mice. Twenty days after transplantation, animals were injected with 1 mCi 99mTc04 and imaged 1 h later.(A) Coronal fusion micro-SPECT/CT slice through the center of the pancreatic tumor (arrow) adjacent to the endogenous stomach activity(arrowhead). Thyroid uptake is also seen on the image. (B) The same imaging data set is displayed as a maximum intensity projection (MIP)generated from threshold-adjusted axial slices. (C) Post-mortem analysis reveals the size and location of the pancreatic tumor (arrow) relativeto adjacent stomach (arrowhead) and other organs.

Mentions:
Additionally, at the CT settings typically employed for small animal imaging, [84, 103] even subcutaneous tumors are only weakly resolved from underlying skeletal muscle, surrounding fluid, and overlying skin. These difficulties in small animal SPECT/CT and PET/CT have resulted in a general bias where tumors for quantitative imaging studies are often much larger than those employed for therapy studies in the same model. In a recent paper [122], we attempted to address these issues by using 1) 1-mm pinhole SPECT collimation, 2) SPECT-based volume of interest (VOI) analysis, 3) empirical tumor-based CT optimization for accurate measurement of in vivo subcutaneous tumor dimensions, and 4) tumor volumes that are more typical of established tumor models for therapy (0.1 to 0.6 cm3). We directly compared the in vivo imaging measurements to ex vivo measurements immediately following imaging. Fig. (2) Using a threshold of 1.5-fold above control tumor uptake (background), we calculated 2.7% MV-NIS-infected BxPC-3 tumor cells were required for detection within this model. Additionally, by measuring the volume of BxPC-3 tumor cells and the tumor cell/stroma ratio, we can calculate that with the imaging settings employed (2.2 mm voxel size), approximately 2 x 105 infected tumors cells are required to reliably resolve a zone of infection from background in this model Fig. (3). We have applied the same general techniques to orthotopic pancreatic tumors stably expressing NIS Fig. (4), and to document multiple sites of MV-NIS injection and infection within a single flank tumor Fig. (3).

Figure 4: Micro-SPECT/CT imaging of an orthotopic transplantation model of pancreatic cancer. BxPC-3-NIS xenograft fragments weretransplanted to the pancreas of donor mice. Twenty days after transplantation, animals were injected with 1 mCi 99mTc04 and imaged 1 h later.(A) Coronal fusion micro-SPECT/CT slice through the center of the pancreatic tumor (arrow) adjacent to the endogenous stomach activity(arrowhead). Thyroid uptake is also seen on the image. (B) The same imaging data set is displayed as a maximum intensity projection (MIP)generated from threshold-adjusted axial slices. (C) Post-mortem analysis reveals the size and location of the pancreatic tumor (arrow) relativeto adjacent stomach (arrowhead) and other organs.

Mentions:
Additionally, at the CT settings typically employed for small animal imaging, [84, 103] even subcutaneous tumors are only weakly resolved from underlying skeletal muscle, surrounding fluid, and overlying skin. These difficulties in small animal SPECT/CT and PET/CT have resulted in a general bias where tumors for quantitative imaging studies are often much larger than those employed for therapy studies in the same model. In a recent paper [122], we attempted to address these issues by using 1) 1-mm pinhole SPECT collimation, 2) SPECT-based volume of interest (VOI) analysis, 3) empirical tumor-based CT optimization for accurate measurement of in vivo subcutaneous tumor dimensions, and 4) tumor volumes that are more typical of established tumor models for therapy (0.1 to 0.6 cm3). We directly compared the in vivo imaging measurements to ex vivo measurements immediately following imaging. Fig. (2) Using a threshold of 1.5-fold above control tumor uptake (background), we calculated 2.7% MV-NIS-infected BxPC-3 tumor cells were required for detection within this model. Additionally, by measuring the volume of BxPC-3 tumor cells and the tumor cell/stroma ratio, we can calculate that with the imaging settings employed (2.2 mm voxel size), approximately 2 x 105 infected tumors cells are required to reliably resolve a zone of infection from background in this model Fig. (3). We have applied the same general techniques to orthotopic pancreatic tumors stably expressing NIS Fig. (4), and to document multiple sites of MV-NIS injection and infection within a single flank tumor Fig. (3).

Bottom Line:
There are several reporter systems available; however, those employing radionuclides for positron emission tomography (PET) or singlephoton emission computed tomography (SPECT) offer the highest sensitivity and the greatest promise for deep tissue imaging in humans.Within the category of radionuclide reporters, the thyroidal sodium iodide symporter (NIS) has emerged as one of the most promising for preclinical and translational research.NIS has been incorporated into a remarkable variety of viral and non-viral vectors in which its functionality is conveniently determined by in vitro iodide uptake assays prior to live animal imaging.

ABSTRACTPreclinical and clinical tomographic imaging systems increasingly are being utilized for non-invasive imaging of reporter gene products to reveal the distribution of molecular therapeutics within living subjects. Reporter gene and probe combinations can be employed to monitor vectors for gene, viral, and cell-based therapies. There are several reporter systems available; however, those employing radionuclides for positron emission tomography (PET) or singlephoton emission computed tomography (SPECT) offer the highest sensitivity and the greatest promise for deep tissue imaging in humans. Within the category of radionuclide reporters, the thyroidal sodium iodide symporter (NIS) has emerged as one of the most promising for preclinical and translational research. NIS has been incorporated into a remarkable variety of viral and non-viral vectors in which its functionality is conveniently determined by in vitro iodide uptake assays prior to live animal imaging. This review on the NIS reporter will focus on 1) differences between endogenous NIS and heterologously-expressed NIS, 2) qualitative or comparative use of NIS as an imaging reporter in preclinical and translational gene therapy, oncolytic viral therapy, and cell trafficking research, and 3) use of NIS as an absolute quantitative reporter.